The present invention relates to a method for positioning a frame in a microfiche microfische retrieval device.
As is well-known, when automatically retrieving a frame recorded on a microfiche with a microfische retrieval device, the target frame is automatically positioned by inputting the address of the frame (expressed by the numbers of frames from the reference frame in row and column) on the keyboard of the retrieval device to make the device convey the microfiche and to detect the frame corresponding to the address so as to be able to project the target frame on a reader screen.
FIG. 1 graphically shows an example of a frame arrangement of a microfiche which has hitherto been used. On this microfiche (m+1) frames are recorded along the horizontal (row) direction X and (n+1) frames are recorded along the vertical (column) direction Y from a "reference frame" P.sub.0 (its address being (0, 0)) which is the first address at the top left corner to a "span frame" P.sub.s (its address being (m, n)) which is the target address at the right bottom corner in the figure. The pitch between adjacent frames is known since it has been specified when photographed. The value is A.sub.x in the direction of the X axis and A.sub.y in the direction of the Y axis. The value is presumed to be manually inputted into the retrieval device in advance.
Conventionally, the reference frame P.sub.0 which is the reference point for positioning frames is first set as the position of projection of the retrieval device. The device measures the distance from the mechanical origin (not shown) thereof by the amount of displacement (for example, the number of pulses) when the film is conveyed and calculates the position of the reference frame P.sub.0 in terms of a coordinate value (X.sub.0, Y.sub.0). When the address of the frame to be retrieved, fore example (i, j) of ".alpha." is inputted, the coordinate value (X.sub.i, Y.sub.j) of the frame ".alpha." is calculated from the following formula (1) using the coordinate value (X.sub.0, Y.sub.0) of the reference frame P.sub.0 and the reference pitches A.sub.x, A.sub.y. ##EQU1##
Such method of positioning, is effective when the pulse number for measuring the position is an integer for each frame. However, some microfiches accompany a pulse fraction per frame. This causes a problem because as the fraction accumulates, an error increases and makes the precise positioning of the object frame difficult. If the size of microfiche varies or the pitch of the frame fluctuates, an error will be caused in the coordinate value thereof to incapacitate precise positioning of the object frame.
Japanese Patent Laid-open No. 195273/1983 discloses a method for positioning a frame by the present applicant which aims at solving the above problems. In the method for positioning a frame, as shown in FIG. 2 which corresponds to the above FIG. 1, the position of the reference frame P.sub.0 is measured in the coordinate values (X.sub.0, Y.sub.0) and that of the span frame P.sub.s in the coordinate values (X.sub.m, Y.sub.n) while the displacements between above two frames L.sub.x and L.sub.y are calculated from the coordinate values by the following formula (2). ##EQU2## The reference pitches A.sub.x, A.sub.y are obtained not from the pitch as explained above but by using the displacements L.sub.x, L.sub.y and the number of frames (m.times.n) from the following formula (3). ##EQU3## When the address of a frame ".beta." to be retrieved, for example, (k, l) as shown in FIG. 2 is inputted, the coordinate values of the frame .beta. (X.sub.k, Y.sub.l) can be calculated from the following formula (4) using the coordinate values (X.sub.0, Y.sub.0) of the reference frame P.sub.0 and the reference pitches A.sub.x, A.sub.y obtained from the above formula (3). ##EQU4##
In this method for positioning the frame, the maximum distances between the exposed frames L.sub.x and L.sub.y of the microfiche are measured as explained above and the maximum distances L.sub.x and L.sub.y are divided by the number of frames to obtain the reference pitches A.sub.x and A.sub.y. Even if the size of the microfiche changes or if the dimension varies, the error becomes extremely small without being accumulated to thereby enable a target frame to be positioned precisely.
In the method, both the reference frame P.sub.0 and span frame P.sub.s have to be photographed. Recorded images have to be very clear since the frames will be used as the reference position as mentioned above. However, some microfiches only have a letter for an index, for example, recorded in the reference frame P.sub.0. Or, since the span frame P.sub.s comes at the very end of the film, some films have nothing recorded in the frame P.sub.s for the convenience of editing. In both cases, they cannot be used as reference frames in positioning. This causes a problem in that the above-mentioned method for positioning a frame is not applicable to such microfilms.